Summary File Change Log for Faster Forever Incremental Backup

1. A method for performing a backup of a file system in a computing environment, the method comprising: initiating a backup operation, by a processor, of the file system, wherein the backup operation is an incremental backup of the file system; identifying files and/or portions of files in the file system to include in the incremental backup by accessing a change log, wherein the change log includes a bitmap file and a data file, wherein the bitmap file includes an entry for each inode in the file system, wherein each of the inodes has an inode number, wherein each entry in the bitmap identifies a corresponding record in the data file that corresponds to one of the inodes and wherein each record in the data file identifies all changes for a corresponding inode, wherein entries included in the records in the data file are created when an event in the file system is detected and wherein not all of the events that change the files or that write to the files result in an entry in the records, wherein a size of the change log is bounded by a number of the inodes in the file system and wherein each bit in the bit map is associated with an inode number and wherein the data file is indexed using the inode numbers; and performing the incremental backup operation based on the change log, wherein all changes in each record are evaluated at the same time prior to performing disk accesses when performing the backup operation such that unnecessary disk accesses are prevented with respect to each record.

2. The method of claim 1 , further comprising accessing the bitmap file to generate a list of files or inodes to be included in the incremental backup operation.

3. The method of claim 2 , wherein inode numbers of inodes in the file system index records in the data file.

4. The method of claim 2 , further processing records in the data file to determine which file in the file system to include in the backup operation.

5. The method of claim 4 , wherein the records identify an old file name, a new file name, an event mask, a file size, and an inode number.

6. The method of claim 5 , wherein processing records comprises evaluating the event mask in each record to determine whether a file access request should be made for the corresponding file.

7. The method of claim 5 , wherein the data file and the map file are sparse files.

8. The method of claim 1 , further comprising purging the change log after the incremental backup operation has been performed.

9. A method for preparing a file system for a backup operation, the method comprising: detecting file events in the file system, wherein the file system is based on inodes, wherein each of the inodes has an inode number; processing the file events to determine whether a files associated with the file events are modified; managing a change log based on the file events that includes a bitmap file and a data file, wherein at least some of the file events result in an entry in the change log, wherein at least some of the file events that modify the files do not result in an entry in the change log, wherein at least some of the file events result in an entry in the bitmap file but not in the data file, wherein the change log associates the file events with the associated inodes, and performing the backup operation based on the change log, wherein all changes in each record are evaluated at the same time when performing the backup operation such that unnecessary disk accesses are prevented with respect to each record.

10. The method of claim 9 , wherein detecting file events further includes detecting modifications to files, the modifications including at least one of a file creation, a file append, a file removal.

11. The method of claim 9 , wherein processing the file events further comprises whether a file event that results in a change to a file that should be included in the backup operation.

12. The method of claim 9 , wherein the change log includes an inode-bitmap file and an inode-data file, wherein the inode-bitmap file contains an on-disk bitmap for each inode number that was modified in the file system since a previous backup and the inode-data file lists actual changes that happen to each file in the file system.

13. The method of claim 12 , further comprising set a bit corresponding to an inode number of a file when the file is removed, where the inode-data file includes a record for the file that stores a full name of the file in an old file name section of the record.

14. The method of claim 12 , further comprising setting a bit in the inode-bitmap file corresponding to a file that is created, wherein the inode-data file includes a record for the file indicating a new name of the file's inode number, wherein the new name is stored in a new file name section of the record.

15. The method of claim 12 , further comprising changing the record of a file that is modified to reflect that the file was modified.

16. The method of claim 12 , further comprising storing records in the inode-data file such that all modifications to an inode number are stored in the same record such that a backup agent can read the record to know all file events related to the file.

17. The method of claim 12 , wherein when a file is created, modified, and then removed, setting a bit in the inode-bitmap file and reading the record for the file in the inode-data file to discover that the file was created, modified and removed.

18. The method of claim 12 , wherein file access requests for files that have been removed are not performed.

19. The method of claim 12 , wherein the inode-bitmap file and the inode-data file are sparse files, wherein each record includes an old file name section, a new file name section, an inode number section, a file size section, and an event mask section.

20. A backup system configured to backup files in a file system by performing incremental backups, the backup system comprising: a backup agent operating on a client to backup a file system, the client including a processor; and a change log stored on a storage device, wherein the change log is associated with inodes in the file system, wherein each of the inodes has an inode number and wherein a size of the change log is bounded by a number of the inodes in the file system, wherein the change log includes: an inode-bitmap file that contains an on-disk bitmap for each inode number that was modified in the file system since a previous backup operation, wherein a number of the bit in the bitmap identifies the inode number and the inode corresponding to the bit; and an inode-data file that includes records for at least some of the inodes in the file system, wherein the inode number is used to index the inode-data file, wherein each record contains sections including an old file name section, a new file name section, an event mask section, an inode number section, and a file size section, wherein the inode-data file lists actual changes that happen to each inode in the file system, wherein the inode-data file is indexed using the inode numbers, wherein at least some events that result in changes to files associated with the inodes in the file system are not included in the inode-data file; wherein the backup agent coordinates with a backup server to perform an incremental backup of the file system based the change log since a most recent incremental backup of the file system, wherein all changes in each record are evaluated at the same time before performing disk accesses for each record when performing the backup operation such that unnecessary disk accesses are prevented with respect to each record.